Nicotinic ACh-receptors in the mammalian central nervous system have been postulated. As yet there is no definitive evidence that these receptors can be labeled or that their activity can be blocked by ligands with the degree of specificity of the snake venom alpha-toxins. Antisera made against nicotinic receptors from skeletal muscle will be tested by sensitive radioimmune assay techniques for their ability to detect brain proteins which share antigenic determinants. A radioimmune inhibition assay employing these sera will be used to test whether alpha-toxin binding is a property of a protein immunologically related to nicotinic receptor. The assay technique to be developed would permit the evaluation of several hereditary and environmental factors on the level of nicotinic receptors in the central nervous system.